Generally the carbon steel barrels are chome plated in the bore. This is not highly thought of as an accuracy improving treatment. That said, most who are shooting comps with the AR are using a Stainless steel barrel. (except the service rifle match, gotta use the chrome bore for that) Colt at one time and maybe still offer an "accurised" top end with a 24" Stainless barrel. They shoot very well BTW.